# Python reverse NumPy array

In this Python tutorial, we will discuss Python reverse NumPy array with a few examples like below:

• Python reverse array sort reverse
• Python numpy inverse array
• Python numpy invert array
• Python numpy flip array

## Python reverse numpy array

• In this section, we will discuss Python reverse numpy array. We can easily use the list slicing() method to reverse an array in Python.
• We create a list in the reverse order as that of the original one.
• Let’s take an example to check how to implement a reverse numpy array
• Basically there are many ways to check reverse numpy array.
• Using list slicing method
• Using flip() function
• Using reverse() function
• Using flipud() method
• Using fliplr() function
• Using length() function

## Using List slicing

In this method first, we will create a NumPy array and then use the slicing method.

Example:

``````import numpy as np

arr= np.array([1, 2, 3, 6, 4, 5])
result = arr[::-1]

print("Reverse array",(result))``````

Here is the Screenshot of the following given code

## Using flip() function

• In this method, we can easily use the Python function flip() to reverse an original array.
• The flip() method is used to reverse the order of values in an array along the given axis.
• The flip() method is defined under the numpy library, which can be imported as import numpy as np, and we can create multidimensional arrays and create other mathematical statistics with the help of the Python numpy module.
• The shape of the numpy array is preferred, but the elements are reordered.

Syntax:

Here is the Syntax of the flip() function

``````numpy.flip
(
arr,
axis=None
)``````
• It consists of few parameters
• arr: input array
• axis: The default, axis=None, will flip all of the axis of the input array. If the axis value is negative it will count the number from the last to the first axis.

Example:

Let’s take an example to check how to implement a reverse NumPy array by using the flip() function.

``````import numpy as np

arr= np.array([9, 8, 3, 6, 2, 1])
result = np.flip(arr)

print("Reverse array",(result))``````

In the above code, we will import a NumPy library and create a NumPy array using the function numpy. array. Now create a variable and assign the function np. flip() in which passes a parameter as an array and prints the result. The result will display in the form of reverse order.

Here is the Screenshot of the following given code

## Using reverse() function

• In this method, we can easily use the function reverse() to reverse an original array.
• The reversed() method always returns the reversed iterator of the given sequence.
• It reverses an array at its original position, hence it doesn’t require any extra space for containing the results.
• It is an inbuilt function in the Python programming language that reverses elements of the list in place.

Example:

Let’s take an example to check how to implement a reverse NumPy array by using the reverse() function.

``````import array

arr=array.array('i',[4,5,9,1,9,3])
print(arr)

#reversing using reverse()
arr.reverse()
print("Reversed Array:",arr)``````

In the above code, we will import a numpy array library and then create an original array and pass array as a parameter

Here is the Screenshot of the following given code

## Using flipud() method

• In this example, we can easily use the flipud() method to reverse an original array.
• The flipud() method is used to flip a given array in the up/down direction.
• Flip the entries in each column and row in the up/down direction.
• The flipud() method is used to shift the function from up to down direction.
• The flipud() means Up / Down. The numpy.flipud() returns a view. Because a view shares memory location with the given array, changing one value from another.

Syntax:

Here is the Syntax of flipud() method

``````numpy.flipud
(
array
)``````
• It consists of few parameters
• array: input array
• Returns: Flipped array in up-down direction

Example:

Let’s take an example to check how to implement a reverse numpy array by using the flipud() method.

``````import numpy as np

arr= np.array([9, 8, 3, 6, 2, 1])
result = np.flipud(arr)

print("Reverse array",(result))``````

In the above code, we will import a NumPy library and then create a NumPy array using the function numpy. array. Now create a variable and assign the method np.flipud in which passes a parameter as an array and prints the result. The result will display in the form of reverse order.

Here is the Screenshot of the following given code

## Using fliplr() function

• In this example, we can easily use the fliplr() function to reverse an original array.
• The np.fliplr() method flips the array in left-right direction. The numpy. flipr() function always accepts a given array as a parameter and returns the same array and flip in the left-right direction.
• It reverses the order of elements on the given axis as 1 (left/right).

Syntax:

Here is the Syntax of fliplr() function

``````numpy.fliplr
(
arr
)``````
• It consists of few parameters
• arr: input array
• Returns: It returns an output numpy array with the columns reversed. Since the function is returned the operation.

Example:

Let’s take an example to check how to implement a reverse NumPy array by using the fliplr() function.

``````import numpy as np

arr= np.array([[3, 5, 6, 7, 2, 1],
[2,5,6,7,8,9]])
result = np.fliplr(arr)

print("Reverse array",(result))``````

Here is the Screenshot of the following given code

## Using length() function

• In this method, we can easily use the length() function.
• We are going to start by pointing to the first element within our list. Take a begin with index variable that is equal to zero. Now, we are going to the end element of our list which is end_index and that’s going to compute the length of our list.
• So the len() function itself is going to return as an integer number

Example:

Let’s take an example to check how to implement a reverse NumPy array by using the length() function.

``````def reverse(nums):

start_index = 0
end_index = len(nums)-1

while end_index > start_index:
nums[start_index],nums[end_index] = nums[end_index],nums[start_index]
start_index = start_index + 1
end_index = end_index -1

if __name__ == '__main__':
n = [1,2,3,4,5]
reverse(n)
print(n)``````

Here is the Screenshot of the following given code

## Python reverse array sort reverse

• In this section, we will discuss Python reverse array sort reverse.
• In Numpy, the np.sort() function does not allow us to sort an array in the largest number order. Instead, that we can reverse an array providing list slicing in Python after it has been sorted in ascending order.
• The slicing method notation [::1] with default start and stop indices and negative step size -1 reverses a given list.
• Use slicing method s[start:stop: step] to access every step-the element starting from index start (included) and ending in index stop.

Example:

``````import numpy as np
arr = np.array([2, 5, 1, 6, 7, 2, 4])

sort_arr = np.sort(arr)
# Reverse the sorted array
reve_arr = sort_arr[::-1]
print(sort_arr)
print(reve_arr)``````
• In the above code, we will import a numpy library and create an array using the numpy.array function. Now create a variable and arrange the elements using the np.sort() function.
• Reverse sorted array using the slicing method and print the output.

Here is the Screenshot of the following given code

## Python numpy inverse array

• In this section, we will discuss Python numpy inverse array.
• For matrix inverse, we need to use numpy.linalg.inv() function.
• This method will inverse the elements in a given matrix. The inverse of a matrix is that if it is multiplied by the original numpy matrix, The output will display in an identity matrix.
• It consists of only one parameter that is Arr and Arr can be a matrix.
• It provides a user easy method to calculate the inverse of the matrix. The function np.linalg.inv() is already available in the Python numpy library.

Syntax:

``numpy.linalg.inv(a)``

Example:

Let’s take an example to check how to inverse an array in python

``````import numpy as np

a = np.array([[4,3],[2,7]])
inverse_matrix = (np.linalg.inv(a))
print(inverse_matrix)``````

In the above code, we will import a numpy library and create an array using the numpy. array function. Now create a variable and assign the function numpy. linalg and display the result.

Here is the Screenshot of the following given code

## Another method to check Python numpy inverse array

• In this method, we can easily use the function np.matrix to inverse the elements of an array.
• It always Returns a matrix from an array-like element (object), or from a string of data.
• A matrix is a specialized 2-Dimension array that contains its 2-D values through operations.
• In this example we use the I attribute to inverse the elements of a given matrix.

Syntax:

Here is the Syntax of np.matrix()

``````numpy.matrix
(
data,
dtype=None,
copy=True
)``````
• It consists of few parameters
• data: it is computed as a matrix with commas or spaces separating columns, and rows.
• dtype: Data type of the matrix

Example:

Let’s take an example to check how to inverse an array in python

``````import numpy as np

m = np.matrix([[4,6],[7,8]])
print (m.I)``````

Here is the Screenshot of the following given code

## Python numpy invert array

• In this section, we will discuss Python numpy invert array. Here we can easily use the function numpy.invert().
• This method is used to compute the bitwise inversion of a given array element-wise.
• It Originates the bitwise NOT of the binary number representation of the integers in the input arrays.

Syntax:

Here is the Syntax of numpy.invert()

``````numpy.invert
(
x,
out=None,
Where=True,
casting='same_kind',
order='K',
dtype=None
)``````
• It consists of few parameters
• X: input array (Only integer value and boolean expression are handled).
• Out: It is an optional parameter. A position into which the result is stored. If provided, it should have a shape function that the inputs broadcast.
• Where: This condition is provided over the input. At a position where the condition is boolean, the out numpy array will be set to the ufunc result.

Example:

Let’s take an example to check how to implement a numpy invert array

``````import numpy as np

arr= np.array([4, 5, 5, 6, 2, 1])
result = np.invert(arr)

print("Invert array",(result))``````

Here is the Screenshot of the following given code

## Python numpy flip array

• In this method, we will discuss the Python numpy flip array. For this, we can easily use the function numpy. flip().
• This method reverses the order of given array elements along the axis, preserving the shape of the array.
• The shape of the array is fixed, but the number of elements is reordered.

Syntax:

Here is the Syntax of the flip() function

``````numpy.flip
(
arr,
axis=None
)``````

Example:

Let’s take an example to check how to implement a reverse NumPy array by using the flip() function.

``````import numpy as np

arr2= np.array([4, 2, 3, 2, 1, 8])
res = np.flip(arr2)

print(res)``````